One of the most common complaints heard about night driving concerns the hazards and discomfort caused by the blinding glare of the headlights of oncoming cars and especially those whose drivers fail to deflect their headlights from high beam to low beam. Also there is incontrovertible evidence that headlignt glare is an important cause of many highway accidents; and with the advent of more powerful cars and higher average driving speeds automobiles are now equiped with headlight lighting systems of increased intensity, in order to extend the range of vision, -- but unfortunately also add to the problem of glare.
U.S. Pat. No. 2,822,488 describes one means used earlier to reduce glare wherein one or more glare-filters are built into a headlight housing between the lens and the conventional tungsten lamp filament -- each glare-filter comprising a sealed ion chamber under partial vacuum and containing an excitable gas or vapor, the latter being energized by high voltage discharge between terminals at opposite extremities of the chamber whenever the primary light source is energized.
While it is alleged that the interposition of the ion chamber (s) between the primary light source and the lens will reduce glare with substantially no loss in illumination nevertheless the construction of a headlight with one or more sealed ion chambers each with its own terminals in addition to the conventional low voltage circuitry for energizing the primary light source presents complex and costly problems of construction not amenable to the economics of mass production technology.
It is desirable therefore to provide modern vehicles with headlights of relatively simple and inexpensive construction which will have the level of illumination required by law and at the same time be substanitally glare-free.